Late Quaternary deep-sea ostracodes in the polar and subpolar North Atlantic:: paleoecological and paleoenvironmental implications

Two sediment cores from the northern North Atlantic. one from the Iceland Plateau and one from the Rockall Plateau. were investigated in order to examine the response of deep-sea benthic ostracodes to climate-related environmental changes since marine isotope stage (MIS) 7. Ostracode fauna was divided into three factor assemblages by using Q-mode factor analyses and diversity was calculated using the Shannon-Wiener index. The Iceland Plateau revealed an 'interglacial assemblage' dominated by Henryhowella, a transitional assemblage dominated by Eucythere, and a 'background assemblage' that consists of the common taxa Krithe and Cytheropteron. The presence of Henryhowella is linked to conditions that prevailed during the peak interglacial periods (MIS 5e and 1), characterized by increased food supply. well-oxygenated bottom water. and lateral advection. The presence of Eucythere, mainly during the interstadial periods. appears to be related to slightly increased food supply, whereas the 'background assemblage' is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times. On the Rockall Plateau the opportunistic 'background assemblage' (consisting mainly of Krithe, Argilloecia, and Cytheropteron) shows no obvious relation to climate changes. The 'interglacial assemblage' consists of several taxa dominated by Pelecocythere but, as on the Iceland Plateau, it also contains Henryhowella. The third assemblage is the 'glacial assemblage' that consists of a variety of taxa. several of which are known from the modern Arctic Ocean and the Greenland Sea shelf. Thus, this assemblage indicates glacial conditions on the Rockall Plateau that are comparable to those found in the present-day Arctic Ocean. Diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg-rafted debris (IRD) in the Rockall Plateau core. Both cores reveal lower surface-water productivity during the glacial compared to the interglacial periods and particularly low productivity during the IRD events, as inferred from carbonate contents. We assume. therefore. that ostracode diversity in the study areas is negatively correlated with food flux. (C) 2002 Elsevier Science B.V. All rights reserved.